A pulverized coal-fired boiler is requested for a reduction in nitrogen oxide (NOx) concentration and to respond to this request, the double burning method is applied. This is a method for burning fuel in the state of insufficient air and then supplying air for complete combustion from an after air port.
For the after air port, to improve the air mixture and burning condition, several structures are proposed. As one of them, an after air port composed of main after air ports and sub-after air ports in which the sub-after air ports are arranged between the main after air ports is known (for example, refer to Patent Documents 1 and 2).
Further, an art for arranging two-stage after air ports on the upstream side and down stream side and controlling the air flow rate and jet direction is disclosed (for example, refer to Patent Documents 3 and 4).
Patent Document 1: Japanese Patent Laid-open No. Hei 5 (1993)-18510 (Abstract)
Patent Document 2: Japanese Patent Laid-open No. 2002-243112 (Abstract)
Patent Document 3: Japanese Patent Laid-open No. Hei 1 (1989)-150707
Patent Document 4: Japanese Patent Laid-open No. Hei 9 (1997)-126415